Bump autoprefixer-rails from 9.6.1.1 to 9.6.4 (#1438)

Bumps [autoprefixer-rails](https://github.com/ai/autoprefixer-rails) from 9.6.1.1 to 9.6.4.
- [Release notes](https://github.com/ai/autoprefixer-rails/releases)
- [Changelog](https://github.com/ai/autoprefixer-rails/blob/master/CHANGELOG.md)
- [Commits](ai/autoprefixer-rails@9.6.1.1...9.6.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Gemfile.lock

@@ -53,7 +53,7 @@ GEM
       rake
       thor (>= 0.14.0)
     ast (2.4.0)
-    autoprefixer-rails (9.6.1.1)
+    autoprefixer-rails (9.6.4)
       execjs
     awesome_print (1.8.0)
     builder (3.2.3)